366 
COMPOSITION  OF  VEGETABLE  GUMS. 
ated.  That  the  adulterant  used  is  generally  vermilion,  but 
sometimes  chrome-red.  That  the  price  of  carmine  is  far  from 
being  a  good  indication  of  its  real  value  ;  and  that  the  only  test 
of  its  true  worth  is  its  apparent  perfect  solubility  in  solution  of 
ammonia  combined  with  richness  and  depth  of  color  in  the 
resulting  solution — London  Pharm.  Journ.  May,  1860. 
ON  THE  COMPOSITION  OF  VEGETABLE  GUMS. 
M.  E.  Fremy*  has  communicated  to  the  French  Academy 
the  results  of  a  very  interesting  and  important  investigation  in- 
to the  constitution  of  the  gums,  and  the  mode  of  their  produc- 
tion in  the  vegetable  organism,  which  opens  up  an  entirely  new 
view  of  the  subject.  He  had  been  led,  by  his  valuable  researches 
on  the  gelatinous  bodies,  and  their  isomeric  transformations, 
which  are  found  present  in  the  utricular  tissues  of  plants,  to 
consider  that  the  gums  might  be  arranged  into  a  series  ©f 
bodies  comparable  to  those  derived  from  pectose  ;  he  therefore 
undertook  their  investigation. 
M.  Fremy  found  that  concentrated  sulphuric  acid  was  capa- 
ble of  effecting  a  complete  modification  of  gum  arabic,  and  of 
converting  into  a  new  body  perfectly  insoluble  in  water.  The 
experiment  is  conducted  in  the  following  manner : — A  mucilage 
of  gum  arabic  is  first  prepared,  so  thick  that  it  will  scarcely  run 
from  the  vessel  containing  it ;  this  is  then  poured  into  a  glass 
containing  concentrated  sulphuric  acid.  The  mucilage  floats  on 
the  surface  of  the  acid  without  any  admixture  taking  place  ;  the 
contact  is  allowed  to  continue  for  several  hours,  and  ultimately 
the  gum  is  found  to  be  transformed  into  a  kind  of  membrane, 
which  is  insoluble  in  boiling  water.  This  substance,  when  prop- 
erly washed,  does  not  retain  a  trace  of  sulphuric  acid.  For 
reasons  which  will  be  more  obvious  presently,  M.  Fremy  names 
this  body  Metagummic  Acid.  This  acid  resists  for  many  hours 
the  action  of  boiling  water,  even  under  pressure ;  but  if  heated 
with  small  quantities  of  any  base,  such  as  the  alkalies  or  alkaline 
Q*M.  Fremy  gives  no  credit  to  Lowenthal  and  Neubauer  who  discovered 
the  acid  nature  of  arabin  in  1855,  see  Chem.  Gazette,  vol.  xiii.  pp.  412, 
from  J  our.  fur  Prakt.  Chem.  lxii.  p.  193.— Ed.  Am.  Jour.  Pharm.] 
